A solid ball is released from rest and slides down a hillside that slopes downward at $65$o from the horizontal. $($a$)$ What minimum value must the coe cient of static friction $($between the surface of the hill and the ball$)$ be for no slipping to occur? $($b$)$ Would the coe cient of friction calculated in case $($a$)$ be su cient to prevent a hollow ball $($such as a soccer ball$)$ from slipping? Explain.